Telescopic bridging plug-pressure set



June 2, 1964 v D, HANEs A3,135,327

TELESCOPIC BRIDGING FLUG-PRESSURE SET 7/Imlllll Il June 2, 1964 v. D. HANEs 3,135,327

TELESCOPIC BRIDGING PLUG-PRESSURE SET Original Filed July 22, 1957 3 Sheets-Sheet 2 Fig.4

Jun 2, 1964 v. DJHANES TELESCOPIC BRIDGING PLUG-PRESSURE SET Original Filed July 22|, 1957 3 Sheets-Sheet 3 j www o llf/IIr\ l.v. u\

3,135,327 TELESCOPIC lilllDGlNG PLUG-PRESSURE SET Vaughan Dean Hanes, West Covina, Calif., assignor to Aerojet-General Corporation, Azusa, Calif., a corporation of Ohio Original application `luly 22, 1957, Ser. No. 673,339, now Patent No. 3,029,872., dated Apr. 17, 1962. Divided and this application Feb. 26, 1962, Ser. No. 185,177 2 Claims. (Cl. 16o-63) This invention relates to oil well tools. More particularly, the invention relates to oil well packers of the type commonly known as bridging plugs. This is a divisional application of my co-pending application, Serial No. 673,339, led July 22, 1957, now Patent No. 3,029,872 patented April 17, 1962, entitled Telescopic Bridging Plug-Pressure Set.

Bridging plugs are employed in oil wells for the purpose of forming a barrier in the well bore. The barrier may be either permanent or temporary, and may be located either in the well casing or in the uncased portion of the well bore. The barrier, thus formed, serves to separate the well bore into upper and lower sections which are isolated from each other. A pressure diiferential may exist across the bridging plug and may vary from a few pounds per square inch to several thousand pounds per square inch.

- The bridging plug of the present invention is intended for use primarily in those cases where the pressure differential across the plug is high.

Heretofore, it has been the practice, when establishing a high pressure barrier in a well, to employ bridging plugs which are relatively large and which therefore contain a large amount of metal which must be drilled up when it is desired to remove them from the well. Such bridging tire job. In recent years, the development of propellantactuated setting tools has made 'possible the running of the plugs on a wire line instead of on pipe, with a consequent large saving in expense.

It is an object of the present invention to provide a bridging plug of the propellant-actuated type, for wire line operation.

Propellant-actuated bridgingplugs of the high pressure type, as heretofore constructed, require the use of separate, detachable setting tools containing the propellantactuated mechanism, which adds to the cost and expense of setting the plugs.

It is an object of the present invention to provide a high pressure bridging plug of the wire line typewhich does not require a separate setting tool and thus reduces the cost and expense of setting the plug.

Heretofore, wire line bridge plugs of the propellant-set type have required the use of insulated electric lines and the associated expensive mobile hoisting equipment for use therewith. The use o f such specialized equipment requires the services of a service company. Ordinary well servicingV crews do not operate such equipment.

It is anobject of the present invention to provide a propellant-set, wire-line bridging plug which does not re-v quire the use of an insulated electric line nor a specially equipped mobile hoisting unit. The bridging plug of the rUnited States Patent O 3,135,327 Patented June 2,` 1964 present invention can be run on the common stranded steel cable which is available on all drilling rigs, workover rigs or well-pulling rigs. No special service crews are required for operation of the bridging plug of the present invention.

Other objects and advantages will be apparent from the following description and drawings disclosing several embodiments of the invention.

FIG. 1 is an elevation, partly in cross section, illustrating one embodiment of the invention in the running-in posiltion, and having only one set of slips.

' FIG. 2 is an elevation, partly in cross section, of the device shown in FIG. 1, in the set position.

FIG. 3 is an elevation, partly in cross section, illustrating the device of FIGS. 1 and 2 equipped with a second set of slips.

FIG. 4 is an elevation, in cross section, of a mechanically actuated firing system for use with the bridging plug,A shown in FIGS. 1, 2 and 3.

FIG. 5 is an elevation, in cross section, of an electrical tiring system for use with the bridging plugs shown in FIGS. 1-3.

FIG. 6 is a continuation of the bridging plugs of FIGS. 4 and 5, showing the lower end thereof.

Referring to FIG. 1, the numeral 1 indicates a well casing. Disposed within the well casing 1 and supported by a wire line, not shown, is bridging plug 2, in the runningin position. The bridging plug 2 comprises live major parts which `are movable relative to each other. These parts are: a piston 3; a cylinder 4; a floating body 5; wedge slips 6; and a compressible packer sleeve 7.

The piston member Sis provided at its upper end with an enlarged head 8 forming a downwardly facing annular shoulder 9, a tubular body 11i having a downwardly depending tubular shank 11 of still further reduced diameter, to which is connected, as by the threads 12, an enlarged, tubular combustion chamber 13.

The edge 13a of combustion chamber 13 forms an out` inwardly turned ilange 15 at its upper end, slidably engalging the exterior surface of the tubular shank' 11. A suitable sealing means, such as an `O ring 16 is mounted` 1n the flange 15 in sealing relation with the outersurface of the shank 11. The lower portion of the cylinder mem-1 ber 4 is enlarged as indicated at 17 to provide an upwardly facing annular shoulder 18 which supports the wedge slips 6 when in their retracted position, as shown in FIG. 1. The'interior of the cylinder 4, below the flange 15 is enlarged to slidably engage the exterior surface of the combustion chamber 13 and to form the pressure chamber 19. Sealing means, such as the 0 ring Ztl,

is positioned in the exterior surfacev of the combustion chamber 13 in sealing engagement between the, walls of the cylinder 4 and the combustion chamber 13.

The pressure chamber 19 communicates with the in-v pellant charge '23. A compression spring 25 vmay be placed between the end of the propellant charge 23 and the end of the combustion chamber 13 to prevent movement of the propellant charge with the attendant danger of breaking the charge. The upper end of the passageway 22 is closed by a Valve member in the form of a small piston 26, slidable in the passageway 22.

' The floating body member 5 is tubular in form with its interior surface 27 in slidable engagement with the exterior surface of the tubular body 10. A uid relief chamber 28 is formed between the interior wall 27 Vof the floating body member and the exterior wall of the shank 11. Ports 29 in the wall of the floating body member 5 communicates the chamber 28 with the exterior of the body vmember 5. The lower portion of the body member 5 is tapered downwardly and inwardly to form a frusto-conical seat 30 for the wedge slips 6. The wedge slips 6 are normally held in their retracted position, resting upon the shoulder 1S, by any suitable means, such as shear pins 31 attached to the body member 5.

The upper end of the floating body member 5 terminates in an upwardly facing annular shoulder 32 which serves as a seat for the lower end of the cylindrical, resilient packer sleeve 7.

In order to lock the members 4 and 13 in extended position, the outer surface of the combustion chamber 13 is provided with a series of vertically spaced, upwardly facing, teeth 33. The teeth 33 are adapted to engage a series of vertically spaced, downwardly facing teeth 34 formed on the inner face of wedge locks 35 mounted in recesses 36 formed in the lower end of the cylinder member 4. The bearing wall 37 of the recess 36 is tapered upwardly and inwardly. A compression spring 33 mounted in a recess 39 in the back of wedge lock 35 tends to force the wedge lock inwardly toward the outer surface of the combustion chamber 13.

The passageway 22 in shank 11 has an upward extension 40 of reduced diameter. The passageway 40 extends to the top of the shank 11 where it communicates with the interior of a tubular housing 41 which is attached to the piston 3 by any suitable means such as the threads 42. The tubular housing 41 contains the mechanism for acuating a firing pin 43 which contacts the percussion cap 24. The firing pin 43 depends from the lower end of piston valve 26. On the upper end of piston Valve 26 is an upwardly extending push rod 44, the upper end of which extends in'to the housing 41. Any suitable means for actuating the firing pin 43-'44 may be utilized, for example, the mechanism illustrated in FIG. 1 that is substantially the same actuating mechanism shown in FIG. 4 and described in detail below.

FIG. 2 illustrates the device of FIG; 1 in set position in the well casing 1. Upon downward movement of the ring pin 43 (FIG. l), the percussion cap 24 is red,

initiating the burning of the propellant charge`23. High spect to the piston 3 pushes the floating body member 5 upwardly. The compressible packer sleeve 7, being restrained by the shoulder 9 on the piston head 8, is compressed and expanded laterally by upward movement of the upper shoulder 32 onv the oating body 5, until the packer sleeve 7 is tightly engaged with the inner wall of the well casing 1. At the same time, upward movement of the cylinder member 4 with respect to the piston 3 causes the teeth 34 on the Wedge lock 35 to engage the teeth 3 on the piston, to lock the cylinder against any subsequent downward movement, and thus maintaining the packer 7 in sealing engagement with the well casing 1. Continued build-up of pressure in the chambers 19 and 13 will cause the bottom of the chamber 13 to be blown out,

releasing the pressure in these chambers. The bottom wall of the chamber 13 is intentionally weakened as indicated at 45, Lfor this purpose. The expanded packer sleeve 7 together with the expanded wedge slips 6 will enable the bridging plug 2 to withstand high differential pressures of several thousand pounds per square inch.

The interior passageways 22 and 40 are closed by the piston valve 26 and also by the housing 41 so that fluid cannot pass through the interior of the bridging plug.

The large metal parts 3, 4 and 5 of the bridging plug are preferably made of a metal which is strong but easily drilled up, for example, cast iron or aluminum. The packer sleeve 7 is preferably made of an oil resistant rubber. The wedge slips 6y are provided with hardened teeth to better engage the interior walls of the well casing 1.

FIG. 3 illustrates a variation of the bridging plug shown in FIGS. l and 2. The plug shown in FIGS. l and 2 has only one set of wedge4 slips 6, these being so positioned as to prevent downward movement of the bridging plug 2 in the well casing 1. Sometimes there exists an upward pressure below the bridging plug which is greater than the downward pressure` from above. In this case it is customary to provide the bridging plug with two sets of wedge slips, one set engaging in a downward direction and the other set engaging in an upward direction. The only changes from the design shown in FIGURES 1 and 2 are: an elongation of the piston body 10a to make room for tubular Wedge seat 46 which slidably surrounds the body extension 10a with its base standing on the packer sleeve '7 and has lits outer surface 47 tapered downwardly to form a seat for wedge slips 48. The wedge slips 48 are normally held in the retracted position by means of shear pins 49. Upward movement of the oating body member 5 relative to the piston body 10a causes the packer sleeve 7 to shear the pins 49 and move the Wedge slips 48 outwardly into engagement with the well casing 1.

FIGURE 4 illustrates one form of actuating device for the bridging plugs shown in FIGURES 1-3. The actuator is of thego-devil type wherein a weight 50 is dropped from the top of the well slidably mounted on the hoisting line 51. The weight 5t) strikes the top of a tubular sleeve 52, forcing it downwardly. The sleeve 52 has a lostmotion connection with a tubular release member 53 which is slidably mounted within the sleeve 52. by means of a cross pin 54 extending radially through sleeve 52 and through a vertical slot 55 inthe release member 53. The lower end of the hoisting line 51 is secured to the upper end of the release member 53 by any suitable means, such as babbitting it into the line socket 56. Suspended on the cross pin 54,.within the tubular release member 53, is a Y cylindrical striker weight 57. The tubular release member 53 is formed with an .upwardly facing external annular shoulder 58 on which is seated a helical compression spring 59. Below the shoulder 53 Vthe tubular release member 53 has an enlarged cavity 60 which releasably receives the upper end of the bridging plug 61. The bridging plug 61 is generally similar to the plugs shown in vFIGURES 1-3 except as to the actuating means for the propellant, as will be described below.

The tubular release member 53 is releasably attached to the upper end of the bridging plug 61 in the following manner. A tubular neck 62 on the upper end of the bridging plug 61 passes slidably through an opening 63 in the lower end of the wall of enlarged cavity .60. An

opening 64 in the wall of the neck 62 receives a retaining surface of a plunger member 67 having a circumferential recess 67a. scribed later.

The cable releasing operation will be depiston members10 and 10a of FIGURES 1-3.

As4 shown in FIGURE 4, initiation of the firing device is accomplished before the releasing of the bridging plug 61 from therhoisting line 51. This initiation is accomplished in the following manner. When the plunger 67 is pushed downwardly by the striker weight 57 (which is accomplished by the falling go-devil 50 striking the sleeve 52), the downward movement of the plunger actuates a tiring pin 69 which strikes a percussion cap 70 in the upper end of an igniter 71 in the upper end of the combustion chamber 72 within the tubular member 73, igniting the propellant (not shown). The upper end of member 73 is attached to the lower end of tubular housing 74 by suitable means such as the threads 75. The tubular housing 74 is Slidably mounted within the bore of a tubular extension 76 whichcorresponds to the tubular The upper end of the tubular extension 76 is counter bored andprovided with a series of vertically spaced, downwardly facing, circumferential `teeth 77 which engage upwardly facing teeth 78 on the outer face of a locking member 79. Locking member 79 has upwardly facing, vertically spaced ratchet teeth 80 which engage a series of vertically spaced, downwardly facing ratchet teeth 81 formed onV the outer surface ofthe tubular housing 74. A shear pin 82 normally locks the members 74 and 76 against relative movement. The tubular housing '74` is provided, near its lower end, with suitable means for sealing the space between the members 74 and 76, such as the vO` rings 83.

The Ytubular housing 74, which is attached to the combustion chamber 72 is divided into upper and lower compartments 84 and 85 by means of a transverse wall 86 having a central opening 87. The plunger 67 is Slidably mounted in the upper chamber 84 and is supported upon a compression spring 88 which rests upon the top of the transverse wall 86. The purpose of the spring 88 is to otiset any tendency for the iiuid submergence pressure to depress the plunger 67 and release the ring pin 69 and tiring the igniter 71, prematurely. The plunger 67 is provided with a downwardly depending'push rod 89 which passes through the opening 87 in the barrier 86. Sealing means, such as the O rings 90 seal the space between the push rod 89 and opening 87. The upper chamber 84 is provided with vent ports 91 to permit the escape of uid as the plunger 67 moves downwardly in the chamber 84. The lower end of push rod 89 is provided with an enlarged, tubular head 92 having a circular opening 93 in its lower end. Slidably received within the opening 93 is a tubular sleeve 94 which houses the iiring pin 69. In the lower chamber 85, between the enlarged head 92 and the under side of the barrier 86 is a compression spring 95 which determines the cable release pressure, as will be explained. t

` The iring pin 69 has an enlarged head 96 having an annular beveled downwardly facing shoulder 96a which normally bears against the upper surface of a ball detent 97 positioned within an opening 98 in the wall of the sleeve 94. A barrier 99 is provided midway of the sleeve 94. There is an opening 100 through the barrier 99 through which the shank of the tiring pin 69 extends. The lower end of the firing pin shank terminates in an enlargedhead V101 which serves as an abutment for a compressed spring 102, the other end of which seats against the under side of the barrier 99. The sleeve 94 is provided with a radially extending flange 103 which is secured between adjoining shoulders on the threadedly joined members 73 and 74. The firing pin 69 is so positioned as to strike the percussion cap 70 when the compressed spring 102 is released'.

The operation of iiringmechanism of FIGURE 4 is as follows: When the go-devil 50 is dropped into the well bore and strikes member S2 the plunger 67 is driven downwardly by the striker weight 57, thus moving the push rod 89 and its enlarged, tubular head 92 downwardly with, respect to the sleeve 94. The upper portion 104 of the interior of the tubular head 92 is of larger diameter than the lower opening 93, with the result that when the ball detent 97 enters the enlarged chamber 104 it releases the head 96 on the upper end of the firing pin 69. The compressed spring 102 then drives the tiring pin downwardly, striking the percussion cap 70 in theigniter 71 and igniting the propellant (not shown) in the combustion chamber 72.

High pressure gas generated by the combustion of the propellant passes upwardly through the combustion chamber 72, outwardly through ports 105 in the wall 73 of the combustion chamber, and into the space between the relatively movable members 74 and 76, causing these members to move in an axial direction with respect to each other.' Such axial movement continues until the packer sleeves 106 and 107 (FIGURE 6) have been expanded by axial compression and wedge slips 108 and 109 have been set. The wedge slips 108 and 109 are normally held in retracted position by shear pins 110 and 111, respectively. Engagement of the ratchet teeth 80 and 81 prevents return movement of the members 74 and 76. Continued generation of pressure in the combustion chamber 72 results in the shearing of the lower end of the combustion chamber 72, as indicated in FIGURES l and 2. The release of the hoisting line 51, carrying the go-devil 50, from the bridging plug 61 is accomplished in the following manner.

The increasing pressure within the combustion chamber 72, due to the burning of the propellant within the chamber, causes the spring 95 to be compressed upward due to the increasing `pressure forcing push rod 89 upward through opening 87. The upward movement of push rod 89 moves plunger member 67 upward. This upward movement continues as the pressure in chamber 72 increases until the recess 67a carried by the plunger member 67 is opposite the cable releasing ball 65 as indicated by dotted lines 68 allowing the ball 65 to fall inwardly into the recess 67a and thereby releases the tubular member 53` from thepacker neck member 62. The entire release member is then withdrawn from the well bymeans of the hoisting cable 51.

FIGURE 5 illustrates an embodiment of the invention in which the bridging plug is adapted to be set by electrical initiation. Electric current is conducted through an insulated electric hoisting line 112 from the top of the well. The bridging plug is shown in the running-in position, with two sets of slips 108 and 109 and two sleeve packers 106 and 107. A spacer ring 113 may be used to separate the sleeve packers 106 and 107, if desired. The lower set of slips 109 are supported on a tubular shoe 114, the outer surface of which is tapered downwardly and inwardly as indicated at 115 to provide a seat for the' wedge slips 109. Shoe 114 is Slidably mounted on a tubular body member 116 which is part of the piston assembly. The tubular body 116 has a partition 117 approximately midway between its ends. A tubular piston rod 118 serves'also as a combustion chamber 119 for the propellant 23a. The piston rod 118 is attached to the partition 117 by any suitable means such as the threads 120 and extended upwardly therefrom. Attached to the upper end of piston rod 118, as by the threads 121, is a tubular" piston 122 of enlarged diameter. The end 122a of piston 122 forms an outwardly projecting ange in conjunction' 125, are mounted between the walls of flange 126 and rod 118. High pressure gas from the burning propellant 23a in the combustion chamber 119 passes through ports 127 in the `wall of the tube 118 and into expansion chamber 123 below the piston 122 and within the cylinder 123, thus forcing the cylinder 123 to move downwardly with respect. to the piston 122. A shear pin 129 secures the piston 122 to the cylinder 123 and prevents premature relative movement between these parts. vRatchet type locking means 136 is provided between the piston 122 and cylinder 123 similar to the locking means described in connection with the device shown in FIGURE 4. A second tubular shoe 131 (46 in FIGURE 4) is slidably mounted on the lower end of the cylinder 123 at which flange 126 is formed and on the upper end of the piston body member 116. is tapered downwardly and outwardly as indicated at 132, to provide a seat for the wedge slips 108. The lower end of shoe 131 rests upon the top of the upper packerv sleeve 1416. Fluid ports 133 are provided in the Wall of the shoe 131 intermediate the ends thereof to permit well Huid to pass in or out of the chamber 134 between the shoe 131 and the tube 118'. In order to force the wedge slips 168 and 169 into engagement with a well casing, the cylinder 123 is provided with an outwardly directed flange 135 having a downwardly facing shoulder 136 which bears The outer surface of the shoe 131 on top and supports the wedge slips 108, and the piston body 116 is provided at its lower end with a similar outwardly directed flange 137 Vhaving an upwardly facing shoulder 13S which bears and supports the lower end of wedge slips 169.

The ignition system shown in FIGURE 5 is different from that shown in FIGURE 4 in that, in FIGURE 5, ignition is accomplished by passing an electric current downwardly through the insulated electric hoisting line 112. The lower end of line 112 is connected to an igniter 139 positioned adjacent the upper end of the propellant 23a. serves also as a piston rod, the lower end, of which is attached to an enlarged guide 141, the latter containing the igniter 139. The guide 141 is normally contained within a cylinder 142 formed by counter boring the upper end' of the tube 118. The guide 141 is normally held in l its lowermost position, as shown, by means of a compression spring 143, the lower Yend of which bears against the top of guide 141 and the upper end of which bears against' Y the extension 143 to seal the space between the inner wall of a bore 152 in the extension 148 and the outer Wall of the tube 14d. The purpose of the seals 150 and 151 is to prevent the passage `of uid to the interior of the bridging plug, past the members 145 and 148. To the upper end of tube 140 is attached an enlarged head 153 which provides means for sealing the inside of tube 140 from outside pressure and also provides means for releasing collar 154 from piston 122. The upper end of the head 153 contains a stufiing ybox 155 having packing means 156-surrounding the line 112 and a threaded follower157 for tightening the packing 156.

When high pressure gas generated by the propellant 23a of FIGURE 5 pushes the tube 140 upwardly, against the pressure of spring 143, through its guide 141 theenlarged head 153 is also pushed upwardly with respect to the tubular piston 122. The upper end of the tubular piston 122 is provided with means for allowing the releasing collar 154 to be detached therefrom. For this purpose, the upper end of the tubular piston 122 is provided with a tubular neck 153 which is slidably received within an opening 159 in the lower end of the releasing collar 154. An opening 160 in the wall of the neck 15S contains a ball detent 161 which has a diameter greater The line 112 is enclosed within a tube 140 which.

than the wall thickness of the neck 158. The ball detent 161 is normally held from inward movement by the head 153 and the inner wall of the releasing collar. The outer, underfacev of the ball detent 161 is supported on an annular upwardly facing shoulder 162 on the inner wall of the releasing collar 154. When the head 153 moves upwardly with respect to the neck 15d, under the influence of high pressure gas, as previously explained, .the head 153 moves above the ball 161, allowing the ball to fall inwardly, inside the neck 15S, thus releasing the collar 154 from the neck 158. The line 112 is a relatively weak line and will be broken as indicated at 163 by the upward pull of the collar 154 after the bridging plug has been set. The collar 154 may be provided with O ring seal 168 to prevent fluid lentering the inside chamber of collar 154.

The upper portion of the releasing collar 154 is provided with means for attaching it securely to the hoisting line 112. lt is customary to provide electric conductor lines such as 112 with several wraps of insulation 164 and an outer sheath of stranded steel wire 165 which carries the load. The outer sheath 165 is passed through a stuffing box 166 into aline socket 167 and the outer wires of the sheath 165 are turned back and/ or imbedded inra body of babbitt or lead` as indicated at 169. Such a construction permits the hoisting line to support a considerable load, on the order cf 6G() lbs., but permits the line toV be pulled out of the socket 167 if the releasing collar 154 should become stuck in the well, thus saving the line and avoiding a fishing job. I

The methods of igniting the propellant and releasing the cable as outlined in the description of FIGURE 4 and FIGURE 5, also provide for a time interval between the igniting of the propellant and the releasing of the hoisting cable. This time interval is provided so that the packer and its slips may be set into holding contact with the casing Wall before the packer is released from the cable. Premature release could allow the packer assembly to fall downwardly in the well bore or casing before the slips have engaged the well casing. In FIGURE 5, this time interval is provided in the following manner.

The propellant 23a, when ignited by means of igniter 139, burns and produces gas withincreasing pressure within the chamber 119 and in the chamber 128 provided between the seals 124 and 125, thus, shearing pins 129, 110 and A111, releasing the slips 16S and 109 and the shoes 114 and 131 between the shoulders 136-and 13S. In-

- creasing pressure within the chamber 12S forces piston 122 upward in relation to cylinder 123 and moves shoulder 11S upward in' relation to shoulder 136. This upward movement compresses the packer sleeves 106 and 107 and expands them outwardly into contact with the well casing (not shown). Further upward movement of the shoulder 138 forces the slips 168 and 109 outward into contact with the casing due to the' tapers 132 and 115 of shoes 131 and 114. The pressure developed within the propellant chamber 119 may increase during the packer setting time interval described above and will increase to higher pressures when the packer sleeves 106 and 107 and the slips 168 and 169 are forced into full contact with the casing, resulting in the release of the collar 154. The collar releasing means, as described in the operation of FIGURE 5, provides pressure responsive means for releasing the collar. A compression spring143 may be provided to prevent the collar from being released from the l@ Y ber in said cylinder, and a fluid passageway connecting 2. In a bridging plug as set forth in claim 1, further said combustion chamber with said expansion chamber; including means associated with said plunger for releasing ignitable propellant means in said combustion chamber; said hoisting lineA from said plug after said plug has been an igniter in said tubular piston and associated with said l set in a Well.

l propellant, spring-pressed percussion means for initiating 5 said igniter; a latch for said percussion means normally References Cited m the me of thls patent holding the percussion means in its retracted position; UNITED STATES PATENTS plunger means for releasing said latch; and means aSSo- 2,807,325 Webb Sept. 24, 1957 ciated With said hoisting line for actuating said plunger. 

1. IN A BRIDGING PLUG ADAPTED TO BE RUN ON A HOISTING LINE AND HAVING A TUBULAR PISTON AND TUBULAR CYLINDER MOUNTED ON AND IN TELESCOPIC RELATION TO EACH OTHER, A COMBUSTION CHAMBER IN SAID PISTON, AN EXPANSION CHAMBER IN SAID CYLINDER, AND A FLUID PASSAGEWAY CONNECTING SAID COMBUSTION CHAMBER WITH SAID EXPANSION CHAMBER; IGNITABLE PROPELLANT MEANS IN SAID COMBUSTION CHAMBER; AN IGNITER IN SAID TUBULAR PISTON AND ASSOCIATED WITH SAID PROPELLANT, SPRING-PRESSED PERCUSSION MEANS FOR INITIATING SAID INGNITER; A LATCH FOR SAID PERCUSSION MEANS NORMALLY HOLDING THE PERCUSSION MEANS IN ITS RETRACTED POSITION; PLUNGER MEANS FOR RELEASING SAID LATCH; AND MEANS ASSOCIATED WITH SAID HOISTING LINE FOR ACTUATING SAID PLUNGER. 